it also marked the first time many americans ever heard the name osama bin laden. of course, september 11th is a critical date not only for the 2001 attacks on america but also the deadly attack on the u.s. mission in benghazi, libya, one year ago. the state department says it's closing 21 u.s. embassies and consulates on sunday out of an abundance of caution. one official telling us the shutdown could be extended beyond sunday. here is our senior international correspondent arwa damon. she's outside the american embassy in cairo. >> reporter: behind this wall is one of the roads that leads to the u.s. embassy in cairo. normally the embassy would have been open on a sunday. it is a working day here. it will, however, be closed because of those security concerns. in the past there have been demonstrations here. there have been mobs, angry mobs, who have gathered trying to attack the embassy. september 11th of last year, for example, an incensed crowd, angered over the film that insulted prophet mohammed, tried to attack the embassy and it was the same day we saw tha